Lamination techniques



cf. 11, 1966 E. s. WENNIN 3,278,354

LAMINATION TECHNIQUES Filed June 20, 1962 INVENTOR Ernest .5. Wen 1m wam ATTORNEY United States Patent "ice 3,278,354 LAMINATION TECHNIQUES Ernest S. Wennin, Emporium, Pa., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed June 20, 1962, Ser. No. 203,819 4 Claims. (Cl. 156-215) This invention generally relates to laminating or film attaching processes and more particularly to the employment of such processes in cathode coating techniques.

In the manufacture of electron tube cathodes, it has been found that pre-cut films of potentially emissive material containing a binder may be adhered to a cathode base material which has been wetted in a fiow or spray operation with a volatile solvent for the binder. Although this process may be used for many coating applications there are some conditions under which the film adherence is not satisfactory. For example, variations in base material, surface conditions may make uniform wetting of this base material diificult to achieve by the wetting operation described above, thereby resulting in imperfections in the film adherence.

An improved process which provides favorable results is disclosed in the co-pending application Serial Number 106,080 filed on April 27, 1961, now US. Patent No. 3,223,569, in the name of William R. McKeirnan et al. and assigned to the same assignee as the present application. As disclosed therein, a vapor chamber may be provided into which the cathode base, the cathode film containing the binder, and a hot solvent vapor are introduced. Upon contact with the hot solvent vapor, the relatively cool cathode base becomes wetted through vapor condensation and the film material, when in contact with the base, softens and tightly wraps itself around and adheres to the cathode base contour. While this improved process has greatly reduced many cathode wrapping problems, it has been found that some cathodes are not ideally wrapped when some solutions having a combination of solvents with a relatively wide range of fractional boiling points are used.

When a solution employing a plurality of individual solvents, each of which has a different vaporization temperature, is boiled from a container to produce a vapor, the solution boils fractionally and intermittent periods of adequate and inadequate vapor production occur. Specifically, as energy in the form of heat is supplied to the multiple solvent solution, the solvent having the lowest boiling point vaporized and this vapor is used to wrap and adhere the film to the cathode base. An additional heat is supplied but before this first solvent is completely vaporized, vapor from the solvent with the second lowest boiling point will be produced and thus the vapor available for the wrapping and adhering process will be a combination of vapors from each of these solvents. This process of producing vapors from each of the various solvents and the ever-changing composition of these vapors will continue until all of the solution has been vaporized. Accordingly, the vapor for the wrapping process is not only continuously changing in composition based upon the presence of individual solvent vapors but also is continuously changing in percentage concentration of each solvent vapor in the composition. In addition, after a major portion of the solvent having the lowest boiling point has vaporized, the energy supplied to the solution will be used as the latent heat of vaporization or the energy necessary to transform the solvent 3,278,354 Patented Oct. 11, 1966 having the second lowest boiling point into a vapor. During the period between final depletion of the first solvents vapors and the generation of vapor having a high concentration of the second lowest boiling point solvent, there will be an inadequate quantity of composite vapor for the wrapping process. This period will then be followed by an adequate quantity of a vapor having a high percentage concentration of this next solvent. Therefore, intermittent periods of adequate and inadequate vapor flow will continue until all of the solution has been vaporized. The problem is further complicated by the resultant change of solvent temperature in the container as new solution is added. Under these circumstances, it is even more difiicult to maintain a continuous and uniform vapor supply over extended periods of production, especially when the individual solvent boiling points in the total solvent solution are relatively broad.

Despite these disadvantages, it has been found that many benefits not heretofore obtainable with a single solvent are provided by a multiple solvent solution. In the attaching process, observation indicates that the vaporization temperatures are important and require control. Further, a vaporization temperature range is pre ferred to a given specific temperature of operation. Therefore, a solvent solution having a plurality of solvents with a range of boiling and condensation points has proven most satisfactory. In addition, it has been found that a satisfactory process for attaching a soluble film on a cathode base or substrate requires a solvent which will weaken the film structure enough to permit its attachment to a cathode base or substrate but yet not attack the film structure so vigorously as to allow its collapse or dispersion into a viscous mass no longer usable as a film. The most effective fulfillment of these requirements to date has proven to be a multiple solvent solution.

It is believed that when a soluble film and cathode base or substrate which has been wetted with a solvent are brought into contact, the solvent, enhanced by the film porosity, penetrates to attack and weaken the film structure at the area of contact by binder dissolution. Accordingly, the cohesive molecular attraction between the solvent and solution molecules existing at the interface and within the weakened film structure provides sulficient force to pull the film and cathode base or substrate into intimate contact. Thus, a multiple solvent solution with its range of characteristics not only provides a latitude of temperature for production purposes but also controls the rate of binder dissolution which is an im portant feature in proper film attachment. These excellent characteristics, when combined with the characteristics afforded by the operating vaporization temperature range of a multiple solvent in a vapor technique, result in an excellent process which can be controlled and maintained for an extended period of time.

Therefore, it is an object of this invention to provide a reliable supply of solvent vapor for wrapping and adhering potentially emissive film material to a cathode base.

Another object of this invention is to control the vapor flow necessary for attaching potentially emissive film material to a cathode base.

An additional object of this invention is to provide a composite vapor from a solvent solution having a plurality of individual solvents, each with a different vaporization temperature, for the wrapping and attachment of a film on a cathode base.

A further object is to enhance the utilization of each individual solvent in a multiple solvent solution during an assembly or laminating operation wherein a film containing a binder soluble in the solution is attached to a substrate which has been wetted with condensed vapors of the multiple solvent solution.

The foregoing objects are achieved in one aspect of the invention by the provision of a vaporization chamber wherein solvents having a plurality of boiling points and solvent properties in a multiple solvent solution are substantially simultaneously vaporized to produce a composite hot solvent vapor. This vapor is condensed upon a relatively cool cathode base or substrate and upon contact with a filrn having a binder soluble in the condensed solvents, the film attaches itself to the cathode base or substrate.

A suspension which may be used in the casting of a film containing potentially emissive material for attachment to a cathode base is disclosed in United States Patent 3,017,281, issued January 16, 1962, to Robert L. Lambert et al. Specifically, the following formulation has been used with excellent results:

Ethylene carbonate gms 200 Toluene ml 400 Ethanol rnl 125 Ethyl acetate ml 50 Butyl carbitol ml 25 Ethyl cellulose ml 35 Barium nitrate gms 4 Triple alkaline earth carbonates gms 400 with the ethyl cellulose having an ethoxyl content of between 47.5 and 49.0% and a viscosity of 300 centipoises in a 5% solution of 80:20 toluene to ethanol.

Although this suspension provides excellent results, it is to be understood that other materials may be used in the suspension as desired to produce a satisfactory film. The butyl carbitol which is defined in Mercks Index, sixth edition, as diethylene glycol monobutyl ether is a temporary plasticizer which is removed during the normal heat and evacuation process of a tube. Other suitable plasticizers include ethylene carbonates, castor oil, and butyl stearate.

Further, the suspension may contain binders other than ethyl cellulose such as nylon, methyl methacrylate, polyvinyl alcohol, and methyl cellulose. In addition, the solvents recited above may be replaced with others well known in the art such as: benzene or xylene for toluene;

acetone, methyl acetate, propyl acetate, or amyl acetate for ethyl acetate; and methanol, propanol, isopropanol, or butanol for ethanol.

This suspension may then be cast into a film of potentially emissive material as disclosed in Unite-d States Patent 2,974,364, issued March 14, 1961 to Robert L. Lambert et al. More specifically, the suspension is flowed onto a support, some of the volatile liquid is then driven off to partially set the film, and the film is subsequently removed from the support. The film is then further dried in preparation for use in the wrapping process. Primarily, a film comprising materials such as alkaline earth carbonates suspended in a volatile soluble binder is provided and, although other suspensions and other film forming processes may be used, excellent results have been obtained with the above mentioned film and casting process.

As mentioned above, the film may be attached to the base member or substrate by bringing the film into contact with the base after it has been wetted with condensed vapors of a solution containing multiple solvents for the film binder. Numerous multiple solvent solutions such as methyl acetate, ethyl acetate, and iso propyl acetate; butyl acetate, iso butyl acetate, and propyl acetate; normal butyl acetate, nonmal butyl ether, and normal butyl alcohol; or Pent-acetate, toluene, and ethanol have provided very satisfactory results in the above mentioned film attachment process but outstanding success has been provided by Pent-acetate as produced by Sharples Chemicals Inc.

Pent-acetate is reportedly made from synthetic amyl alcohol and produced by hydrolysis of amyl chloride obtained by the chlorination of pentane. It is a mixture of five isomeric amyl acetates, N-amyl acetate, 2-methyl butyl acetate, 3-methyl butyl acetate, 4-methyl butyl acetate, and 3-ethyl propyl acetate, and similar to the amyl acetate derived from amyl alcohol found in fusel oil but in addition contains some n-amyl and sec-amyl acetates. Its low specific heat (0.491) and relatively wide boiling range (126-155 C.) provide a satisfactory range of operating temperatures as compared with a single solvent. Additionally, its alcohol content provides improved solvent strength which can be readily released from the film in an air drying process. Further, this solution appears to be among the safest of lacquer solvents available for production processes. Specific properties of Pent-acetate may be found in the following references: Industrial Solvents" 2nd edition by Ibert Mellan (Reinhold Publishing Corporation, 1950) pp. 712-715; and The Technology of Solvents by Arthur K. Doolittle (John Wiley and Sons Inc.), pp. 571-573.

For a better understanding of the present invention, together with other and further objects, advantages and capabilitie thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a cathode base and attached film of potentially emissive material;

FIG. 2 is a perspective view of a cathode base in contact with a film of potentially emissive material prior to attachment;

FIG. 3 is a diagrammatic view of an apparatus for attaching a film to a cathode base or substrate; and

FIG. 4 is a diagrammatic view of a modified apparatus for attaching a film to a base.

Referring to the drawings, a cathode base 10, which is conventional and-may be formed from a metal such as nickel or an alloy thereof, is shown in FIG. 2 prior to attachment but in contact with a potentially emissive film 8. Cathode base 10 may be wetted at a discrete area only with a volatile solvent solution such as the Pentacetate previously described and the potentially emissive film 8 may then be touched or blown thereto for tacking purposes. The film will remain substantially as shown in FIG. 2 until it can be conveyed to an attachment area, designated generally as position 11 of FIG. 3. Although this method of conveying both cathode base 10 and potentially emissive film 8 to attachment area 11 has been found expedient in production, the cathode base 10 and potentially emissive film 8 may be conveyed separately and joined at attachment area 11 to provide a film wrapped cathode base as shown in FIG. 1.

Generally, in a process for attaching a substrate or cathode base with a film such as one containing potentially emissive material, a solvent solution like that indicated by the numeral 12 in FIG. 3 is supplied to a vaporization chamber 22 wherein a hot solvent vapor is produced from the solution. In practice, a conveyor 40, having spaced cathode base attachment means 42, operates to transport (in the direction of the arrow) a relatively cool cathode base 10 and contacting film 8 through a hot solvent vapor attachment area 11. Base 10 may be above or below ambient temperature prior to entering area 11, but in any event it should be sufficiently cool relative to the temperature range of the solvent vapors to provide readily the vapor condensation thereon. Within attachment area 11 the hot solvent vapor condenses on and wets the relatively cool cathode base whereupon the film 8 attaches itself to cathode base 10 to produce the structure shown in FIG. 1. As the attached film and cathode base progress through the hot solvent vapor, the temperature of cathode base 10 gradually rises whereupon the condensed solvent in the film is substantially volatilized and the film satisfactorily dried. Should conveyor 40 move sufiiciently fast to remove the attached film and cathode base from attachment area 11 before the film has satisfactorily dried, an auxiliary heating chamber 32 having heating elements 34 mounted therein may be used to complete the drying operation.

In detail, a multiple solvent solution 12 such as Pentacetate is gravity fed from container 14 through attached tubing 16 and dripped from restricted orifice 20 onto a heated chamber surface 26. The rate at which solution 12 is deposited upon heated chamber surface 26 is adjusted by flow control valve 18.

Referring to FIGURE 3, the vaporization chamber 22 wherein the hot solvent vapor is generated is provided with an entrance 28 for tubing 16 through which the multiple solvent solution 12 is transferred. The heated chamber surface 26 is preferably positioned substantially perpendicular to the dripping solution 12. A heating element 24, which may be energized by a power supply 23 and regulated by a variac 25 or other well known means provides adjustable control over the temperature of surface 26. This heating element 24 and its power source are formed to supply sufiicient energy to raise the temperature of surface 26 above the highest boiling point of any solvent in the multple solvent solution. In addition, sufiicient heat energy is supplied to maintain this required surface temperature as solvent solution 12 at room temperature is dripped or otherwise placed thereon at a rate suflicient to produce the quantity of hot solvent vapor required for adequate film attachment. An exit orifice 30 is provided through which the generated hot solvent vapor is directed to attachment area 11. Therefore, by controlling the amount of multiple solvent solution placed on heated surface 26 with flow control valve 18 and by controlling the temperature of surface 26 with adjustments provided for heating element 24, optimum film attachment may be obtained. Thus the utilization of this apparatus, a multiple solvent solution having an operating temperature range and controlled rate of film binder dissolution is placed into contact With a heated chamber surface so that the solvents of the solution are substantially simultaneously vaporized to produce a composite hot solvent vapor of controllable quantity available for condensation and production of the composite solvent solution desired for attachment of a film to a base.

An alternate form of vapor producing apparatus is diagrammatically illustrated in FIG. 4 in which a multiple solvent solution 43 such as Pent-acetate is gravity fed from container 44 through a pipe 46 to any conventional type of continuously operating pumping means 48. This pump preferably receives a constant supply of multiple solvent solution 43 and provides a pulsating flow of solution 43 through conduit 50 to a solution chamber 52. Attached to solution chamber 52 is an injection device such as a hypodermic needle 54 having a restricted orifice 56 through which the desired amount of solution 43 from solution chamber 52 is dispensed onto heated chamber surface 62. Solution chamber 52 has an attached pipe 58 and control valve 59 through which solution in excess of the amount desired for dispersion onto heated chamber surface 62 is returned to container 44. The flow rate of the excess solution back to container 44 is determined by control valve 59 thereby also controlling the dispensing rate of the solvent to chamber surface 62. The hypodermic needle 54 is mounted within vaporization chamber 60 through an entrance aperture 66 and is positioned substantially perpendicular to the heated chamber surface 62.

A heating element 64 which is connected to a conventional power source 65 through a variable control 67 provides sufiicient energy to chamber surface 62 to raise and maintain its temperature above the boiling point of any solvent in multiple solvent solution 43. Solution 43 is dispersed onto chamber surface 62 at a rate sufiicient to produce the quantity of hot solvent vapor required for adequate film attachment. In addition, a tube 70 is attached to vaporization chamber 60 at exit orifice 68 through which the hot solvent vapor 69 is directed to an attachment area. Tube 70 may be provided with an encircling heating element 72 having a conventional power source 71 and variable control 73. Sufficient energy is supplied to heating element 72 to permit transfer of the composite solvent vapor generated to an attachment area Without alteration of vapor composition. Thus, a process and apparatus is provided in which a multiple solvent solution having a vaporization temperature range is substantially simultaneously vaporized into a composite vapor and this composite vapor remains substantially unchanged until ready for condensation and use in the process of attaching a film to a substrate or cathode base.

Although the laminating or attaching technique described herein has been specifically illustrated in conjunction with a cathode base and electron emissive film it is to be understood that this invention is not limited thereto and can be used to attach any type film containing a soluble binder to another material or substrate which has been wetted with condensed vapors of a solvent solution for the binder.

While there has been shown and described what are at present considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. In a process for attaching at a given position a film containing a soluble binder to a relatively cool base which has been wetted with condensed vapor of a solvent solution for the binder, said solution including a plurality of individual solvents wherein at least one solvent has the highest temperature of vaporization and at least one solvent has the lowest temperature of vaporization which is above the relatively cool base temperature comprising the steps of substantially simultaneously generating, within a confined space, a vapor including all of said solvents, and directing said solvent vapor to the given attaching position in an unconfined atmosphere while maintaining said vapor at least at said highest solvent vaporization temperature to provide condensation upon and solvent wetting of the relatively cool base to promote attachment of said film to said base when in contact with one another.

2. In a process for attaching at a given position a film of potentially emissive material containing a volatile soluble binder to a relatively cool cathode base which has been wetted with condensed vapor of a volatile solvent solution for the binder, said solution including a plurality of individual volatile solvents wherein at least one solvent has the highest temperature of vaporization and at least one solvent has the lowest temperature of vaporization which is above the relatively cool cathode base temperature comprising the steps of substantially simultaneously generating, within a confined space, a vapor including all of said solvents, and directing said solvent vapor to the given attaching position in an unconfined atmosphere while maintaining said vapor at least at said highest solvent vaporization temperature to provide condensation upon and solvent wetting of the relatively cool cathode base to promote attachment of said film of potentially emissive material to said cathode base when in contact with one another.

3. In a process for applying potentially emissive material on a cathode base in the form of a film having a soluble binder, said binder being soluble in a multiple solvent solution having one solvent with a boiling point higher than the boiling point of any other solvent in the solution, the steps comprising heating a surface to at least the boiling point of said solvent having the highest boiling point in the solution from a thermal source capable of maintaining said surface above said higest solvent boiling point while producing vaporized solvent Within a confined space at a given rate, and applying a multiple solvent to said surface at or below said given rate to provide solvent vapor for application to said film, said film being located in a free atmospheric space whereby said film is attached to said cathode base when in contact therewith.

4. In a process for attaching a film having a volatile binder soluble in a multiple solvent solution to a relatively cool base, wetted with said solution, the steps comprising substantially simultaneously generating, within a confined space, a vapor comprising all solvents in the multiple solvent solution, and directing said vapor to an attachment area in the free atmosphere whereat the hot solvent vapor condenses on the relatively cool base to promote attachment of said film to said base when in contact therewith.

8 References Cited by the Examiner UNITED STATES PATENTS EARL M. BERGERT, Primary Examiner.

W. B. WALKER, J. P. MELOCHE, Assistant Examiners. 

1. IN A PROCESS FOR ATTACHING AT A GIVEN POSITION A FILM CONTAINING A SOLUBLE BINDER TO A RELATIVELY COOL BASE WHICH HAS BEEN WETTED WITH CONDENSED VAPOR OF A SOLVENT SOLUTION FOR THE BINDER, SAID SOLUTION INCLUDNG A PLURALITY OF INDIVIDUAL SOLVENTS WHEREIN AT LEAST ONE SOLVENT HAS THE HIGHEST TEMPERATURE OF VAPORIZATION AND AT LEAST ONE SOLVENT HAS THE LOWEST TEMPERATURE OF VAPORIZATION WHICH IS ABOVE THE RELATIVELY COOL BASE TEMPERATURE COMPRISING THE STEPS OF SUBSTANTIALLY SIMULTANEOUSLY GENERATING, WITHIN A CONFINED SPACE, A VAPOR INCLUDING ALL OF SAID SOLVENTS, AND DIRECTING SAID SOLVENT VAPOR TO THE GIVEN ATTACHING POSITION IN AN UNCONFINED ATMOSPHERE WHILE MAINTAINING SAID VAPOR AT LEAST AT SAID HIGHEST SOLVENT VAPORIZATION TEMPERATURE TO PROVIDE CONDENSATION UPON AND SOLVENT WETTING OF THE RELATIVELY COOL BASE TO PROMOTE ATTACHMENT OF SAID FILM TO SAID BASE WHEN IN CONTACT WITH ONE ANOTHER. 